Yingzi Fu

Electrochemical enantioselective recognition of tryptophane enantiomers based on chiral ligand exchange

Electrochemical enantioselective recognition of tryptophane (Trp) enantiomers in the presence of Cu(II) using L-cysteine (L-Cys) self-assembled gold electrode is described. The chiral recognition of Trp enantiomers was investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM). Time dependencies of the enantioselective interaction for the L-Cys modified electrodes with Trp enantiomers solutions in the presence of Cu(II) were also studied. The results showed that L-Cys had stronger interaction with D-Trp than L-Trp in the presence of Cu(II), and the discrimination was caused by the selective formation of Cu complexes with L-Cys and Trp enantiomers relying on the principle of chiral ligand exchange. The structure of the Cu complexes was optimized by the hybrid density functional theory (DFT) method. And the enantiomeric composition of L- and D-Trp was monitored by measuring the current responses of the sample.

The application of thionine–graphene nanocomposite in chiral sensing for Tryptophan enantiomers

The thionine-graphene (THi-GR, positively charged) nanocomposite was successfully synthesized as a good biocompatible matrix for ds-DNA which acted as a chiral selector to construct an electrochemical chiral biosensor for Tryptophan (Trp) enantiomers sensing with the assistance of Cu(II). The nano-bionic interface was constructed as follows: Firstly, the nanocomposite was dropped on the surface of glassy carbon electrode (GCE), and then ds-DNA (negatively charged) was immobilized onto the nanocomposite film via the opposite-charged adsorption techniques. This biofunctionalized nanocomposite was characterized with scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) spectrometry and cyclic voltammetry (CV). The chiral biosensor was employed to study the recognition effect between ds-DNA and Trp enantiomers by CV. The results show that larger electrochemical response was obtained from l-Trp when Cu(II) was present, indicating this strategy could be employed to enantioselectively recognize Trp enantiomers. Under optimum conditions, the chiral biosensor exhibited a good linear response to Trp enantiomers in the range of the concentration of [Cu(II)(Trp)2] from 5.0 × 10(-4) to 2.5mM with a low limit of detection of 0.17 μM (S/N=3). The binding constant was calculated to be 2.97 × 10(3)M(-1) for [Cu(II)(l-Trp)2] and 2.50 × 10(2)M(-1) for [Cu(II)(d-Trp)2].

Coupling of a Reagentless Electrochemical DNA Biosensor with Conducting Polymer Film and Nanocomposite as Matrices for the Detection of the HIV DNA Sequences

Abstract This paper describes a reagentless electrochemical DNA biosensor applied to the detection of human immunodeficiency virus (HIV) sequences based on electrochemical impedance spectroscopy (EIS). The novel DNA biosensor has been elaborated by means of an opposite‐charged adsorption Au‐Ag nanocomposite to a conductive polymer polypyrrole (PPy) modified platinum electrode (Pt) and self‐assembly the mercapto oligonucleotide probes onto the surface of modified electrode via the nanocomposite. The duplex formation was detected by measuring the electrochemical impedance signal of nucleic acids in phosphate buffer solution (PBS). Such response is based on the concomitant conductivity changes of the PPy film and nanocomposite. The reagentless scheme has been characterised using 21‐mer synthetic oligonucleotides as models: parameters affecting the hybridization assay were explored and optimized. The detection limit is 5.0×10−10 M of target oligonucleotides at 3σ. The potential for development of reagentless DNA hybridization analysis in the clinical diagnosis is being pursued.

A sensing interface for recognition of tryptophan enantiomers based on porous cluster-like nanocomposite films

A sensing interface with porous cluster-like nanocomposite films has been fabricated by electrochemical polymerization of L-cysteine on the surface of multi-walled carbon nanotubes (PLC/MWCNTs), and it was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The nanocomposite films have been used to interact with tryptophan enantiomers (D- and L-Trp), and an obvious difference was achieved in the oxidation peak currents between D-Trp and L-Trp, suggesting that the PLC/MWCNTs could be used as a chiral selector to discriminate the Trp enantiomers. Under the optimum conditions, D-Trp and L-Trp presented a detection limit of 33 μM (S/N = 3), with a linear range of 1.0 × 10−4 M to 1.0 × 10−3 M. The simple method with rapid recognition, excellent stability and reproducibility provided a new perspective to recognize and determine Trp enantiomers.

Enantioselective recognition of mandelic acid based on γ-globulin modified glassy carbon electrode.

A new chiral biosensor has been fabricated by immobilizing γ-globulin on gold nanoparticles modified glassy carbon electrodes, which could recognize and detect mandelic acid (MA) enantiomers. Differential pulse voltammetry, quartz crystal microbalance, ultraviolet-visible spectroscopy, and atomic force microscopy were used to characterize the enantioselectivity. The results exhibited that γ-globulin modified electrode could enantioselectively recognize MA enantiomers, and larger response signals were obtained from R-MA. The factors influencing the performance of the resulting biosensor were investigated. The enantiomeric composition of R- and S-MA enantiomer mixtures could be determined by measuring the current responses of the sample. The developed electrodes have the advantages of simple preparation, good stability, and rapid detection.

A reagentless enantioselective sensor for tryptophan enantiomers via nanohybrid matrices

A reagentless method for the selective electrochemical discrimination of tryptophan (Trp) enantiomers has been developed by means of adsorbing human serum albumin (HSA) onto a methylene blue–multi-wall carbon nanotubes nanohybrid (MB–MWNTs) modified glassy carbon electrode (HSA/MB–MWNT/GCE). Cyclic voltammetry (CV) was employed to monitor the immobilization processes and the electrochemical behavior of the Trp enantiomers on the HSA/MB–MWNT/GCE. It was found that the newly developed electrode exhibited different interactions toward the Trp enantiomers, with a stronger binding effect obtained between HSA and L-Trp. The linear range of the biosensor was investigated from 1.0 × 10−1 to 1.0 × 10−8 mol L−1 with a detection limit of 3.3 × 10−9 mol L−1. In addition, the values of the enantioselectivity coefficient (α) and the association constant (k) were calculated. This work appears to provide a reference for the development of a reagentless electrochemical chiral biosensor and improves understanding of the high selectivity between biological molecules and chiral amino acids.

Chiral sensing for electrochemical impedance spectroscopy recognition of lysine enantiomers based on a nanostructured composite

A simple and reliable chiral sensing platform for enantioselective recognition of lysine (Lys) enantiomers based on a nanostructured composite (NC) via the electrochemical impedance spectroscopy (EIS) technique was described. The NC has been successfully synthesized through covalent linkage among the semiconductor 3,4,9,10-perylenetetracarboxylic acid (PTCA), thionine (Thi) and chiral selector L-N-tert-butoxycarbonyl-O-benzylserine (L-BBSer). The stepwise synthesis process of the NC was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and EIS. The enantioselective interaction assay between NC modified glassy carbon electrode and lysine enantiomers relied on EIS technology. As a prototype example, good recognition results were obtained from the difference of electron transfer resistance (ΔRet), where ΔRetD was larger than ΔRetL and linear responses in ΔRet were found for Lys enantiomers ranging from 100 nM to 10 mM with a detection limit of 33 nM (S/N = 3). In addition, the results of analyzing another four amino acids revealed the specificity of the proposed sensor. The developed sensor with the advantages of simple preparation, long-term stability, good sensitivity and commendable selectivity, holds great potential application for the nanostructured composite adulterated with a chiral selector in chiral bio-electroanalysis.

Chiral recognition of penicillamine enantiomers using hemoglobin and gold nanoparticles functionalized graphite-like carbon nitride nanosheets via electrochemiluminescence.

A new stable and stereo-selective electrochemiluminescence (ECL) interface has been designed for specific recognition of penicillamine (Pen) enantiomers by using hemoglobin (Hb) and gold nanoparticles functionalized graphite-like carbon nitride nanosheets composite (Au-g-C3N4 NHs) modified glassy carbon electrodes (Hb/Au-g-C3N4/GCE). The advantages of Hb as chiral selector and Au-g-C3N4 NHs as luminophore were perfectly displayed in this novel interface. The obviously different ECL intensity was exhibited after l-Pen and d-Pen adsorbed on Hb/Au-g-C3N4/GCE, and a larger response was observed on d-Pen/Hb/Au-g-C3N4/GCE. Under the optimum conditions, the developed ECL chiral sensor showed excellent analytical property for detection of Pen enantiomers in a linear range of 1.0×10-4M to 5.0×10-3M, and the detection limits of l-Pen and d-Pen were 3.1×10-5M and 3.3×10-5M (S/N=3) respectively. This work with high selectivity, stability and reproducibility may open a new door based on ECL to discriminate Pen enantiomers.

A new chiral electrochemical sensor for the enantioselective recognition of penicillamine enantiomers

A new chiral electrochemical sensor has been successfully prepared through chemical linking l-methotrexate (l-Mtx) onto the gold electrode surface. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the enantioselective interaction between l-Mtx and Pen enantiomers. The results showed that the l-Mtx-modified gold electrode can selectively recognize penicillamine (Pen) enantiomers using Zn(II) as central ion, and larger response signal was observed from d-Pen owing to the selective formation of Zn complexes. The interaction time between the modified electrode and Pen enantiomers containing Zn(II) was considered. And the electrochemical response of the modified electrode to a series of different concentration of Pen in the presence of Zn(II) was also monitored. In addition, the enantiomeric composition of d- and l-Pen enantiomer mixtures was monitored by measuring the current responses of the sample.

Enantioselective recognition of penicillamine enantiomers on bovine serum albumin-modified glassy carbon electrode

As a natural chiral selector, bovine serum albumin (BSA) has been used to recognize penicillamine (Pen) enantiomers through electrochemical methods. The recognition and assay rely on the stereoselectivity of BSA embedded in ultrathin Al2O3 sol–gel film coated on the surface of glassy carbon electrode (BSA/GCE). The enantioselective interaction between Pen enantiomers and BSA was monitored by cyclic voltammetry and electrochemical impedance spectroscopy measurements, from which larger response signals were obtained from d-Pen. The factors influencing the performance of the modified biosensor were also investigated. The association constant (K) was calculated to be 1.93 × 104 L mol−1 for d-Pen and 1.20 × 103 L mol−1 for l-Pen. A good linear response was exhibited with the concentration of Pen enantiomers by BSA/GCE over the range of 1 × 10−8–1 × 10−1 mol L−1 with a detection limit of 3.31 × 10−9 mol L−1.